Cigarette smoking is causally associated with cancer of the lung, larynx and esophagus and increases the risk for cancer of the pancreas, kidney and urinary bladder and, likely, the cervix. Pipe and cigar smoking which increases the risk for lung cancer to a lesser degree, is causally associated with cancer of the larynx, oral cavity and esophagus. Exposure to environmental tobacco smoke (ETS) gives rise to some risk of cancer. Snuff- dipping is causatively related to cancer of the oral cavity and pharynx; chewing of tobacco may be associated with oral cancer. Betel quid chewing with tobacco is carcinogenic to humans, without tobacco it is less so. Cigarette mainstream smoke (MS) and its particulate matter induce benign and malignant tumors in laboratory animals. Bioassay data on the carcinogenic activity of sidestream smoke (SS), ETS and snuff, chewing tobacco, and betel quid are needed. To elucidate problems in tobacco carcinogenesis, we propose I) continuation of the development of sensitive quantitative assays for globin- and DNA-adducts with tobacco-specific N- nitrosamines (TSNA) and application to analysis of blood samples, exfoliated oral cells and oral cavity punch biopsy samples from smokers, passive smokers and snuff-dippers; II) refinement of analytical methods for TSNA and synthesis and bioassays of newly identified TSNA; application of appropriate methods to MS, SS, ETS and snuff profile analysis; study of the endogenous formation of nitrosamines in smokers and chewers; III) delineation of the formation of 3-(methylnitrosamino) propionitrile (MNPN) during betel quid chewing, and of factors that influence the formation of areca- and tobacco-specific nitrosamines; study of the binding of MNPN metabolites to DNA, of the metabolism of the betel quid alkaloid, arecoline, development of an immunoassay for its major metabolite and application to saliva, blood and urine analyses of betel quid chewers; IV) determination of aromatic amines and their metabolites in the urine of smokers, passive smokers and nonsmokers and development of an immunoassay for o-toluidine in urine; V) elucidation of the chemical nature of biologically active flavor components in the smoke of cigarettes, and in snuff; VI) bioassay for carcinogenicity of SS and studies on the uptake of SS and ETS by active and passive smokers; analysis of biological fluids of passive smokers for tobacco-specific markers and determination of such markers in stored biological fluids of presumed nonsmokers with lung cancer.